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New random number generator (wip)
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//#############################################################################
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//# Function: Random number generator
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//# Function: Random number generator #
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//#############################################################################
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//# Author: Andreas Olofsson #
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//# License: MIT (see LICENSE file in OH! repository) #
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//#############################################################################
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module oh_random
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#(parameter N = 32, //width of counter (max value)
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parameter SEED = 32'haaaaaaaa //non zero number to start with
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#(parameter N = 32 //support multiple of 32 for now...
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)
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(
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input clk,
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input nreset, //async reset
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input [N-1:0] mask, //mask output (1 = active)
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input en, //enable counter
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input en, // enable counter
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input entaps, // enable taps input
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input [N-1:0] taps, // user driven taps
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input [N-1:0] seed, // seed
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input [N-1:0] mask, // mask output (1 = active)
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output [N-1:0] out //random output pulse
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);
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wire [N-1:0] taps_sel;
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reg [N-1:0] lfsr_reg;
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wire [N-1:0] lfsr_in;
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// TODO: support non-multiples of 32
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reg [N-1:0] lfsr_reg[0:N/32-1];
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wire [N-1:0] lfsr_in[0:N/32-1];
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wire [N-1:0] taps_sel[0:N/32-1];
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wire [N/32-1:0] feedback;
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// LFSR tap selector (TODO: complete table)
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// instantiate multiple 32bit rngs
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genvar i,j;
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generate
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case(N)
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32: assign taps_sel[31:0] = 32'h80000057<<1;
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endcase // case (N)
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for(i=0;i<(N/32);i=i+1) begin
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//taps
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assign taps_sel[i] = entaps ? taps[(i+1)*32-1:i*32]: 32'h80000057 << 1;
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//lfsr reg
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always @(posedge clk or negedge nreset)
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if(~nreset)
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lfsr_reg[i] <= seed[(i+1)*32-1:i*32];
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else if(en)
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lfsr_reg[i] <= lfsr_in[i];
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// feeback
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assign feedback[i] = lfsr_reg[i][31];
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assign lfsr_in[i][0] = feedback[i];
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for(j=1;j<32;j=j+1) begin
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assign lfsr_in[i][j] = taps_sel[i][j] ? (lfsr_reg[i][j-1] ^ feedback[i]) :
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lfsr_reg[i][j-1];
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end
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assign out[(i+1)*32-1:i*32] = mask[(i+1)*32-1:i*32] & lfsr_reg[i];
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end // for (i=0;<N/32;i=i+1)
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endgenerate
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// counter
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always @(posedge clk or negedge nreset)
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if(~nreset)
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lfsr_reg[N-1:0] <= SEED;
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else if(en)
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lfsr_reg[N-1:0] <= lfsr_in[N-1:0];
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assign feedback = lfsr_reg[N-1]; //feedback from MSB
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assign lfsr_in[0] = feedback; //unconditional feedback for [0]
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genvar i;
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for(i=1;i<N;i=i+1)
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assign lfsr_in[i] = taps_sel[i] ? (lfsr_reg[i-1] ^ feedback) :
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lfsr_reg[i-1];
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assign out[N-1:0] = mask[N-1:0] & lfsr_reg[N-1:0];
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endmodule // oh_random
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